U.S. patent application number 13/256873 was filed with the patent office on 2012-01-19 for method and device for determining a foreign substance content in a matrix.
This patent application is currently assigned to CRINOTEC GMBH. Invention is credited to Andreas Fiedler.
Application Number | 20120015449 13/256873 |
Document ID | / |
Family ID | 42269983 |
Filed Date | 2012-01-19 |
United States Patent
Application |
20120015449 |
Kind Code |
A1 |
Fiedler; Andreas |
January 19, 2012 |
METHOD AND DEVICE FOR DETERMINING A FOREIGN SUBSTANCE CONTENT IN A
MATRIX
Abstract
A method and a device are provided for determining a content of
at least one foreign substance in a matrix of a solid or liquid
food. At least one reagent area for providing at least one reagent
has a receptacle for a replaceable reagent container for
replaceably connecting a sample container including at least the
matrix; a transfer line is provided between the reagent area and
the reaction area, by which the at least one reagent can be fed to
the reaction area; a sensor area is provided for demonstrating the
foreign substance released from the matrix; a carrier gas line is
provided between the reaction area and the sensor area, by which
the released foreign substance can be fed to the sensor area; and
an output line is provided through which the dissolved foreign
substance can be fed outward from the sensor area.
Inventors: |
Fiedler; Andreas;
(Rottenburg a. N., DE) |
Assignee: |
CRINOTEC GMBH
Tubingen
DE
|
Family ID: |
42269983 |
Appl. No.: |
13/256873 |
Filed: |
December 14, 2009 |
PCT Filed: |
December 14, 2009 |
PCT NO: |
PCT/EP2009/008936 |
371 Date: |
September 15, 2011 |
Current U.S.
Class: |
436/501 ;
422/430; 422/547; 422/69; 422/82.01; 422/82.05; 436/20 |
Current CPC
Class: |
G01N 2035/00811
20130101; G01N 33/0042 20130101; G01N 33/146 20130101 |
Class at
Publication: |
436/501 ; 436/20;
422/82.05; 422/547; 422/69; 422/82.01; 422/430 |
International
Class: |
G01N 33/02 20060101
G01N033/02; G01N 27/00 20060101 G01N027/00; B01L 3/00 20060101
B01L003/00; G01N 33/14 20060101 G01N033/14; G01N 21/75 20060101
G01N021/75 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 19, 2009 |
DE |
10 2009 013 534. |
Claims
1. Device (100) for determining a content of at least one foreign
substance (89) in a matrix (88) of a solid or liquid food,
characterised by at least one reagent area (40) for providing at
least one reagent (58) with a receptacle (41) for an
interchangeable reagent container (50); one reaction area (60) with
a connection system (62) for interchangeable connection of a sample
container (80) at least containing the matrix (88); one transfer
line (13) between the reagent area (40) and the reaction area (60),
with which the at least one reagent (58) can be transferred to the
reaction area (60); one sensor area (90) for the detection of the
foreign substance (89) released from the matrix (88); one carrier
gas line (15) between the reaction area (60) and the sensor area
(90), through which the released foreign substance (89) can be
transferred to the sensor area (90); and one output line (17)
through which the dissolved foreign substance (89) can be
transferred from the sensor area (90) outwards.
2. Device according to claim 1, characterised in that the reagent
area (40) comprises at least one sensor device (55) which
automatically detects a presence or absence of the at least one
reagent (58) and/or reagent container (50) in the reagent area
(40).
3. Device according to claim 1 or 2, characterised in that the
reagent area (40) has a receptacle (41) which accommodates the one
reagent container (50).
4. Device according to any one of the above claims, characterised
in that for connection of the reagent container (50) the reagent
area (40) has a needle system (48) to which the reagent container
(50) is attachable, in particular wherein the needle system (48)
has at least one input-side hollow needle (42) and one output-side
hollow needle (44) or a hollow needle with an inner hose.
5. Device according to any one of the above claims, characterised
in that, for connecting a sample container (80), the reaction area
(60) has a feed system (62), through which at least the reagent
(58) can be fed and released foreign substance (89) can be
discharged.
6. Device according to any one of the above claims, characterised
in that a sensor can be inserted into a headspace (86) of the
sample container (80).
7. Device according to any one of the above claims, characterised
in that the reaction area (60) has a heating and/or cooling
device.
8. Device according to any one of the above claims, characterised
in that the sensor area (90) houses an electrochemical sensor (92),
in particular wherein the electrochemical sensor (92) comprises a
reference electrode (93) with a chloride-free redox system,
preferably Pb/PbSO.sub.4.
9. Device according to any one of the above claims, characterised
in that the sensor area (90) comprises a photometric sensor.
10. Device according to any one of the above claims, characterised
in that the carrier gas line (15) between the reaction area (60)
and sensor area (90) is divided into a first branch line (15a) for
supplying carrier gas to the sensor area (90) and a second branch
line (15b) for bypassing the sensor area (90).
11. Interchangeable reagent container (50) for a device (100) for
determining a content of foreign substance (89) in a matrix (88)
according to any one of the above claims, which is prepared ready
for use with a defined quantity of at least one reagent (58), and
which is interchangeably connectable to the receptacle (42) of the
reagent area (40).
12. Reagent container according to claim 11, characterised in that
one or more codings (52) are provided to detect the presence in the
device (100) of the contained reagent (58) and/or its nature.
13. Reagent container according to claim 11 or 12, characterised in
that in addition to the reagent (58), a corrosion inhibitor is
contained.
14. Interchangeable sample container (80) for a device for
determining a content of foreign substance (89) in a matrix (88)
according to any one of claims 1 to 12, which is prepared ready for
use and can be interchangeably connected to the connection system
(62) of the reaction area (60), wherein at least one member of the
group contained is (a) an adduct former (84) in metered quantity
that is matched to the foreign substance (89) to be detected and
which serves for binding of any foreign substance (89) dissolved in
the matrix (88); (b) a substrate (83), which dissolves in contact
with a reagent (58) and/or a matrix (88) (c) a chemical component
with a positive enthalpy of solution, so that the chemical
component absorbs heat when dissolving in the matrix, in particular
wherein the adduct former (84) is pyruvic acid or a salt of pyruvic
acid, and/or in particular wherein the reagent (84) comprises
sulphuric acid and/or phosphoric acid.
15. Sample container according to claim 14, characterised in that
the substrate (83) comprises a substance that is capable of forming
a network, in particular a three-dimensional network, preferably
agar and/or gelatine.
16. Set, comprising a reagent container (50) according to any one
of claims 11 to 13 and a sample container (80) according to any one
of claims 14 to 15 for use in a device (100) for determining a
content of at least one foreign substance (89) in a matrix
(88).
17. Method for operating a device (100) for determining a content
of at least one foreign substance (89) in a matrix (88) of a solid
or liquid food, according to any one of claims 1 to 10,
characterised in that an originally dissolved foreign substance
(89) in the reaction area (60) in the matrix (88) is first bound
and the foreign substance (89) originally dissolved in the matrix
(89) is released with a delay such that the originally dissolved
foreign substance (89) and any originally bound foreign substance
(89) are released from the matrix together in the same process
step.
18. Method according to claim 17, characterised in that for delayed
release the matrix (88) containing the foreign substance (89) is
mixed with an adduct former (84) to bind dissolved foreign
substance (89) and that after binding of the originally dissolved
foreign substance (89), a reagent is added, which drives the
originally dissolved foreign substance (89) and any foreign
substance originally bound (89) out of the matrix (88).
19. Method according to claim 18 or 19, characterised in that for
delayed release the matrix (88) containing the foreign substance
(89) is covered and/or a polymerisation is carried out, in
particular wherein the driven-out foreign substance (89) is fed by
a carrier gas to a sensor (92) for detection of the foreign
substance (89).
20. Method for determining a content of at least one foreign
substance (89) in a matrix (88) of a solid or liquid food,
characterized in that an originally dissolved foreign substance
(89) in a matrix (88) is first bound and a foreign substance (89)
originally dissolved in the matrix (89) is released with a delay
such that the originally dissolved foreign substance (89) and any
originally bound foreign substance (89) are released from the
matrix together in the same process step and the determination of
the content of the foreign substance (89) released in the same
process step is carried out through a sensor (92).
21. Method according to claim 20, characterised in that to delay
the release of foreign substance (89) an adduct former (84) is
added that binds the dissolved foreign substance (89).
22. Method according to claim 20 or 21, characterised in that a
reagent (58) is added for release of the foreign substance
(89).
23. Method according to claim 21 or 22, characterised in that the
adduct former (84) contains pyruvic acid or a salt of pyruvic acid
and the reagent contains sulphuric acid and/or phosphoric acid.
24. Method according to claims 20 to 23, characterised in that the
matrix (88) is a liquid and/or solid food, in particular wine,
fruit juice, beer or dried fruits, and the foreign substance (89)
is bound and/or dissolved SO.sub.2.
25. Use of one or more reagents (58) and/or one or more adduct
formers (84) which are suitable for carrying out a method according
to any one of claims 20 to 24 for testing of liquid and/or solid
foods, in particular wine, fruit juice, beer, dried fruit.
Description
BACKGROUND AND SUMMARY
[0001] The invention relates to a method and device for determining
the content of a foreign substance in a matrix according to the
preamble of the independent claims.
[0002] It is of interest in various fields to know the content of a
foreign substance that is in a matrix, for instance a liquid
sample, and that is free and/or bound to constituents. One such
component is, for example, sulphur dioxide (SO.sub.2), the content
of which is to be determined, for instance, in wine. The presence
of SO.sub.2 in fruit juices or other foods, including those of
solid consistency, also cannot be neglected for health reasons.
[0003] Furthermore, SO.sub.2 is of importance in environmental
analysis, for example in control systems for exhaust air, flue gas
desulfurization and determination of the maximum permissible
workplace concentration etc.
[0004] The legislator has now laid down maximum values for many
areas of SO.sub.2 usage which must be met by industry, producers
and filling facilities and which consequently must be checked at
regular intervals.
[0005] It is only possible to do without SO.sub.2, for example in
wine production, to a certain degree, because SO.sub.2 is used, for
example, to treat the wine barrels, and also serves as a
preservative and is generally regarded as an indispensible
component for high-quality wine production. Nevertheless, SO.sub.2
has adverse health effects that manifest themselves, for example,
through severe headaches after drinking wine with high
concentrations of SO.sub.2.
[0006] In addition, for wine in particular there are a large range
of wine faults and wine diseases which are caused by unwanted or
excessive concentrations of components.
[0007] This includes, for example, the odour caused by the presence
of acetic acid, "Boeckser" aroma caused, inter alia, by hydrogen
sulphide, the cork taint caused by 2,4,6-trichloroanisole and the
woody taint caused by 3-methyl octano-4-lactone.
[0008] For further information on components causing wine faults
and wine diseases see Rompp Lexikon Chemie [Rompp's Lexicon of
Chemistry], 10th Edition, 1999, Georg Thieme Verlag, Stuttgart.
[0009] Sulphur dioxide/sulphurous acid is present in wine, both
free and bound to various constituents. The total content of
sulphurous acid is represented by the sum of all state forms, which
must be monitored in terms of certain maximum values. The presence
of bound SO.sub.2 is mainly due to the so-called bisulphite
addition to aldehydes and ketones.
[0010] A whole range of measurement methods are known to determine
free sulphuric acid or free SO.sub.2 from statutory analysis
specifications and from corresponding manuals for wine growers. A
distinction is drawn between so-called reference methods and rapid
methods. The known reference methods are very time consuming,
require complex apparatus and are correspondingly expensive.
Analyses using rapid methods are inaccurate and are poorly
reproducible because of numerous interference parameters. One
problem is that ascorbic acid is very often present in wine and,
for example, is incorrectly identified as sulphurous acid in
iodometric methods, which are classed as a titrimetric method and
are amongst the recognised rapid methods. To determine the
concentration of free sulphurous acid, it is necessary to determine
the concentration of ascorbic acid separately and to subtract this
from the value obtained.
[0011] In addition to iodometry it is also known to determine
SO.sub.2, for example, using colorimetry, oxidation methods, gas
measuring electrodes, enzymatic methods or through gas
chromatography.
[0012] To allow bound sulphurous acid to be determined by the known
methods it is necessary to release it through alkaline
saponification or by heat through a recognized reference method
such as distillation with strong acids, which necessitates
additional, costly and time-consuming process steps which,
moreover, are not always quantitatively sufficiently reliable.
[0013] In gas chromatography, for example, using a flame photometer
or an electrolytic Hall detector, the SO.sub.2 concentration is
measured in the headspace above the liquid sample, then Henry's law
is applied to calculate the concentration of sulphurous acid in
solution. Henry's Law, also known as Henry's law of absorption,
states that the vapour pressure of a dissolved substance is
proportional to its mole fraction in an ideal diluted solution. The
proportionality is expressed by an empirical, temperature-dependent
Henry's constant. Although the measurement with subsequent
calculation results in a satisfactory outcome, the use of a Hall
detector or a flame photometer is, however, limiting for the method
given. Both the cost and the required experimental experience for
the use of the specified detectors limit its application to large
specialist facilities. For smaller wineries, bottlers or analytical
laboratories, the use of the known method is not viable.
[0014] The procedures described so far for sulphur dioxide analysis
thus require a substantial investment of time and equipment
expense, and are particularly disadvantageous in that other
components are also determined at the same time, so that these must
be measured separately and subtracted from the obtained measured
value.
[0015] A simplified device and a method for measuring the content
of SO.sub.2 in wine is known from EP 1285 266 B1, in which the wine
is aerated by a carrier gas that is passed in a short circuit
through the wine. This gives rise to an equilibrium state so that
the concentration of SO.sub.2 present in the gas phase can be
detected and evaluated by means of an electrochemical cell. Gas
feed can be automated during sample preparation. The method
delivers sufficiently good results. A device is known from EP 1 840
557 with which the composition of liquids can be determined.
Reagents are introduced into a reagent area and the reagents added
with metering to a sample in a reaction area, which liberates
constituents in a head space or forms a volatile compound with
them. The composition can be determined qualitatively and
quantitatively in that absorption spectra of the gas in the head
space are recorded and the absorption behaviour of the gas is
analysed.
[0016] U.S. Pat. No. 3,873,273 A discloses an automated system for
testing blood samples. The presence of blood samples is established
and optical transmission properties of the blood samples, to which
a reagent is added, are investigated.
[0017] WO 83/00932 discloses an apparatus for the storage and
delivery of reagents. Reagent containers are attached to container
receptacles of a carrier, wherein during the attachment process a
needle penetrates a pierceable septum in the container
receptacle.
[0018] The aim of the present invention is to create a further
improved method and device with which less experienced people can
also detect the presence of a foreign substance in a matrix on
site.
This aim is achieved through the features of the independent
claims. The other claims, the drawings and description describe
favourable embodiments of the invention.
[0019] A device is proposed for the determination of the content of
at least one foreign substance in a matrix of a solid or liquid
food, that has at least one reagent area for provision of at least
one reagent with a receptacle for an interchangeable reagent
container, a reaction area with a connection system for connecting
the sample container at least containing the matrix, a transfer
line between the reagent area and the reaction area, with which the
at least one reagent can be transferred to the reaction area, and a
sensor area for the detection of the foreign substance released
from the matrix, a carrier gas line between the reaction area and
the sensor area, with which the released foreign substance can be
transferred to the sensor area, and an output line through which
the dissolved foreign substance can be transferred from the sensor
area outwards.
[0020] The reagent container and/or sample containers are
advantageously prefabricated and already pre-filled with chemical
components that are exactly matched to one another in terms of
nature and quantity. Particularly preferably, they are configured
so that they can be used in the device without the danger of
mix-ups. The user only needs to introduce the matrix to be
investigated, possibly containing a foreign substance, in a
pre-determined quantity. For example, a vintner can check the
sulphite (SO.sub.2) content of the wine in the wine cellar.
SO.sub.2 in this case represents the foreign substance and wine is
the matrix. However, it is also possible to analyse sulphur-treated
dried fruit that is broken into small pieces and mixed, for
example, with water, and to analyse fruit juices, beer and the
like. Food is to be understood here as substances and products that
humans ingest for the purpose of nutrition or enjoyment by mouth,
possibly after prior preparation. This in general includes food,
beverages, food additives and food supplements. Similarly,
feedstuffs for animals can also be subsumed under it.
[0021] Hereinafter, SO.sub.2 refers to the sulphite content, which
may be present in dissolved form or bound in the matrix. Dissolved
SO.sub.2 is also referred to as free SO.sub.2. The device can
advantageously be used for the detection of free SO.sub.2 alone and
for the detection of the total content of SO.sub.2, which is
present in the food in dissolved and bound form.
[0022] The reagent area may advantageously comprise at least one
sensor device that automatically detects a presence or absence of
the at least one reagent and/or the presence of a reagent container
in the reagent area. Similarly, the type of reagent in the reagent
container can additionally be detected. The sensor device can, for
example, be a light barrier that detects a coding on the reagent
container, a barcode, an RFID encoding (Radio Frequency
IDentification), a lever, a micro switch and the like.
[0023] The reagent area can advantageously have a receptacle for
receiving a reagent container, preferably, the reagent container
can be fully contained in the receptacle. The reagent container can
be inserted in a carrier housing and with the carrier housing can
be inserted in the reagent area. As a result, the reagent container
can be handled more easily and together with the carrier housing
can be removed easily from the receptacle. The carrier housing can
be configured to hermetically seal the receptacle, which increases
the safety of the device. The reagent container can, for example,
be configured as a pierceable ampoule with a pierceable septum as a
closure, or be sealed with a welded-on or glued-on metal or plastic
film.
[0024] The reagent area can have a needle system for attachment of
the reagent container, onto which the reagent container can be
attached. The needle system can preferably comprise at least two
hollow needles, which are immersed in the reagent container. One
needle preferably represents the inlet to the reagent container,
which can be connected, for example, to a transport device, for
example a pump or reservoir, the other represents an outlet, which
can be connected, for example, to the reaction area. The needles
can also extend to different depths into the reagent container. The
longer needle is first to come into contact with the interior of
the reagent container. The longer needle preferably represents the
outlet for the reagent. As a result, any excess pressure in the
reagent container upon connection of the reagent container can
reliably transport the reagent in the desired direction to the
reaction area, if this is connected via the longer needle to the
reagent area. The needle system can comprise needles arranged in
parallel, or the needles can be arranged coaxially, for example a
shorter needle can be inserted into a longer needle. Alternatively,
a hollow needle with an inner hose can also be provided.
[0025] Additionally or alternatively, a check valve can be provided
on the input side, thereby ensuring that the reagent can only leave
the reagent container in a desired direction, even if the needles
extend the same distance into the reagent container. In addition,
the needles can be advantageously configured as a modular unit so
that the needles can be readily exchanged. For this, the needles
can be integrated into a block that has the appropriate connection
possibilities for a transport means and for a connection to the
reagent area.
[0026] The reaction area can advantageously have a feed system for
connection of a sample container through which at least the reagent
can be fed. The released foreign substance can preferably be
dischargeable through the feed system and, for example, be passed
to the sensor. The feed system can be configured as a needle
system. It is also conceivable, however, to provide hoses or small
tubes. For this, a parallel arrangement of needles and/or hoses
and/or tubes lying next to one another, as well as a coaxial
arrangement, is possible. The feed system can preferably be guided
through a stopper, which can serve as splash protection and can
also seal the sample container when it is connected to the reaction
area. The sample container is preferably attached to a cone-shaped
pin, from which the feed system with the plug projects. A sealing
ring or a sealing lip for sealing of the attached sample container
can be disposed on the pin. This allows the sample containers to be
readily and reliably docked to the reaction area.
[0027] A sensor is advantageously introducible into a headspace of
the sample container. This can be provided alternatively, or
additionally, to a sensor in a sensor region at a distance from the
sample container.
[0028] The reaction area can have a heating and/or cooling device.
This allows the detection reaction to be advantageously suitably
supported. The heating can be achieved, for example through
external components such as a heating coil in the sample, heating
of the line system, heating through radiation (for example
infrared, microwaves), a heating jacket around the sample
container, addition of substances that release heat upon
dissolution etc. Similarly, in addition or alternatively, a use of
reagents in the sample container is possible which because of their
aggressiveness do not require additional heating, or which
themselves release heat upon contact with a substance or the
sample. Cooling can be carried out by external components or
through the addition of substances that consume heat upon
dissolution. An uncooled reaction is also conceivable.
[0029] The sensor area can preferably comprise an electrochemical
sensor. The electrochemical sensor favourably comprises a reference
electrode with a chloride-free redox system. The reference
electrode preferably comprises a Pb/PbSO4 system. This allows a
reference potential to be made available for the electrochemical
sensor, to which the measured potential can be compared. The
reference electrode system is favourably free of chloride and the
system has a long-term stability of at least one year when
installed. The sensor allows a simple and non-critical handling and
is in particular stable in an acidic environment. There is in
particular no "bleeding" of the system through concentration
differences. A disturbance or poisoning of the foreign
substance-sensitive working electrode of the electrochemical sensor
can be avoided. If, depending on the chemical system, it is
intended to work in the alkaline range, then the reference
electrode system can be appropriately selected.
[0030] Alternatively or additionally, the sensor area can comprise
a photometric sensor and/or provide other conventional detection
methods.
[0031] According to an advantageous development of the device a
carrier gas line between the reaction area and sensor area can be
divided into a first branch line for supplying carrier gas to the
sensor area and a second branch line to bypass the sensor area. For
substances, such as the reagent, which can dry out a membrane or a
layer of the sensor that reacts on the substance, an excessive
exposure of the membrane can be avoided without a detrimental
effect on measurement accuracy. Furthermore, the flow properties
can be optimized. Since the gas does not have to flow directly past
the membrane, advantageous diffusion-controlled quasi-static
conditions can develop at the sensor area/at the membrane.
Fluctuations in the gas flow can thereby be compensated for, which
has a positive effect on measurement accuracy. This is advantageous
if the carrier gas has time-varying concentrations of the analyte
so that the concentrations at the sensor vary over time.
[0032] According to another aspect of the invention an
interchangeable reagent container for a device for determining a
content of foreign substance in a matrix of a solid or liquid food
is proposed, which is provided in ready-to-use form with a defined
quantity of at least one reagent for use in the device and can be
connected interchangeably to the receptacle of the reagent area.
One or more codings can be provided to detect the presence in the
device and/or the nature of the contained reagent. The at least one
reagent can be an acid, preferably at least one acid selected from
the group of sulphuric acid, phosphoric acid and hydrochloric
acid.
[0033] Depending on the type of matrix and foreign substance to be
investigated, other inorganic or organic acids and/or other
concentration ranges of the acids may be favourable. An alkaline
reagent is also conceivable if it is intended to work in the
alkaline range. Consequently, for the detection of SO.sub.2 in wine
for example, an alkaline hydrolysis is also conceivable to split
bisulphite adducts with subsequent expulsion of SO.sub.2 in an
acidic environment.
[0034] The reagent container can advantageously have a corrosion
inhibitor added to it. Thus, for the detection of sulphite in wine,
a 50-85% sulphuric acid mixture can be modified by iron (III) salts
such that the hollow needles of the needle system in the reagent
area are not chemically attacked or only to a negligible degree. In
addition to iron (III) salts, other salts are suitable, such as
those of copper, tungsten or molybdenum, for example,
Al.sub.2(SO.sub.4).sub.3
MnSO.sub.4*1aq
ZnSO.sub.4*7aq
FeSO.sub.4*7aq
CoSO.sub.4*7aq
H.sub.3[P(Mo.sub.3O.sub.10).sub.4]*xH.sub.2O
NiSO.sub.4*6H.sub.2O
SnCl.sub.2*2H.sub.2O
CuSO.sub.4*5aq
Fe.sub.2O.sub.12S.sub.3*x aq
Bi.sub.2(CO.sub.3).sub.3
Na.sub.2MoO.sub.4*2H.sub.2O
Na.sub.2WO.sub.4*2H.sub.2O
VOSO.sub.4*5H.sub.2O.
If a plurality of reagents are used in the device, such as in the
determination of free SO.sub.2 and bound SO.sub.2 in wine, then the
various reagents can be mixed with the inhibitor to maintain a
defined concentration of inhibitor.
[0035] According to another aspect of the invention an
interchangeable reagent container for a device for determining a
content of foreign substance in a matrix of a solid or liquid food
is proposed, and can be connected interchangeably to the connection
system of the reaction area, wherein at least one member of the
group is (a) an adduct former in a metered quantity that is matched
to the foreign substance to be detected and which serves to bind
any dissolved foreign substance in the matrix, (b) a substrate that
dissolves in contact with a reagent and/or a matrix, and (c) a
chemical component with positive enthalpy of solution, so that the
chemical component absorbs heat upon being dissolved in the
matrix.
[0036] The sample container is in particular matched in its
dimensions to the device and the reagent and sample quantities
used. Measurement errors due to incorrect dosages can thus be
avoided.
[0037] One adduct former can favourably be contained in a metered
quantity. The adduct former is present to bind any dissolved
foreign substance present in the matrix. In this way previously
dissolved, i.e., "free" portions of the foreign substance in the
matrix and the previously chemically bound portions of the foreign
substance in the matrix can be released later virtually
simultaneously.
[0038] Favourable adduct formers are in particular molecules with
aldehyde and/or ketonic functions, possibly also in ring form
(e.g., sugar). Alternatively, adsorbents can be used which can bind
the foreign substance to their surface. Alternatively, other
substances can be used which bring about the retention of a foreign
substance, for example an oily layer, polymerisation upon sample
addition (wine addition) and/or addition of acid etc.
Polymerisation can be achieved for example through condensation of
benzyl alcohol or its esters with strong acid, i.e., addition of
benzyl alcohol to the sample, whereby polymer formation commences
upon introduction of the acid.
[0039] The adduct former can preferably be matched to the foreign
substance to be determined, such as SO.sub.2. For detection of
SO.sub.2, pyruvic acid, or a salt of pyruvic acid, preferably a
sodium salt of pyruvic acid, is preferred as the adduct former.
[0040] The sample container can, additionally or alternatively,
contain a substrate that comprises a substance that is capable of
forming a network, in particular a three-dimensional network, such
as agar or gelatine. The substrate can dissolve in contact with a
reagent and/or a matrix and ensure mixing of reagent and adduct
former. The substance can, for example, be a complex-forming
polymer, a chelating agent or a gel. The substrate can be formed in
particular by the substance. The skilled person will choose a
suitable substrate depending on the specific boundary conditions
and materials. By dissolving the substrate in contact with a
reagent and/or a matrix, an advantageous mixing of the sample,
i.e., matrix with foreign substance and the adduct former and/or
the reagent can be achieved. The analytical times can thereby be
advantageously reduced. Mixing can conceivably be carried out as an
alternative or additionally through stirring, vibration and the
like.
[0041] In addition or alternatively, a chemical component with a
positive enthalpy of solution can advantageously be present in the
container. This can bring about cooling of the sample container, in
particular for the detection of free SO.sub.2.
[0042] According to a further aspect of the invention a set is
proposed, comprising a reagent container and a sample container for
use in a device for determining the content of at least one foreign
substance in a matrix of a solid or liquid food. The reagent
container can advantageously contain an acid to release the bound
foreign substance and the sample container can contain an adduct
former that is matched to a foreign substance to be detected. The
reagent container is filled ready for use with a suitable reagent
to detect a foreign substance in a matrix. The sample container is
similarly filled ready for use and can contain at least one member
of the group
(a) an adduct former in a metered quantity that is matched to the
foreign substance to be detected; (b) a substrate that dissolves in
contact with a reagent and/or a matrix; (c) a chemical component
with a positive enthalpy of solution. Optionally, heating can be
achieved through a component with negative enthalpy of solution or
reaction enthalpy.
[0043] A method is proposed for operation of a device for
determining a content of at least one foreign substance in a matrix
of a solid or liquid food, wherein an originally dissolved foreign
substance is first bound in the reaction area in the matrix and the
foreign substance originally dissolved in the matrix is released
with a delay, such that the originally dissolved foreign substance
and any foreign substance originally bound are released together
from the matrix in the same process step. This is carried out in
particular in the determination of a total content of SO.sub.2,
which is present in the matrix in dissolved and bound forms.
[0044] The matrix can advantageously be mixed with an adduct former
for binding of the dissolved portion of foreign substance. After
binding of the originally dissolved foreign substance a reagent can
be added which drives out the originally dissolved foreign
substance and any originally bound foreign substance from the
matrix. The driven-out foreign substance can preferably be fed
through a carrier gas to a sensor for the detection of the foreign
substance.
[0045] Alternatively, it is also conceivable, instead of adding an
adduct former, to cover the matrix, to hold back a foreign
substance released early and to only release it when the portion of
the foreign substance originally bound in the matrix is released.
It is also conceivable to combine the addition of an adduct former
and the covering of the matrix.
[0046] Since measurement, for example of the SO.sub.2 content in
wine is not carried out in chemical equilibrium, different
time-dependent concentration profiles for different
sulphate-containing species, bound to different extents, are to be
expected. It has been found that sulphite present in the wine
sample as free SO.sub.2 exhibits a time-shifted forwardly displaced
peak in the measurement curve for concentration, which falls
relatively rapidly after reaching the maximum concentration. For
species in which the chemical equilibrium lies very much on the
side of the bound SO.sub.2, curves can be seen in which the peak in
the time-dependent
concentration profile is shifted in time strongly backwards and the
fall after the maximum concentration is relatively slow. According
to an aspect of the invention, with the delayed release of the
originally unbound foreign substance from the form bound to the
adduct former even in the presence of very different species in
unknown concentration ratios it is possible to equalise the
concentration profile for simple mathematical determination of the
concentration via the sum of all species of the particular foreign
substance, for example the sulphite species in wine, dried fruit,
fruit juices, beer and the like.
[0047] In the detection of total foreign substance content in the
matrix, which is present originally in dissolved and bound form,
the foreign substance adduct can be transformed again into the
educts (adduct former and foreign substance) through heat and acid
influence. By means of a gas stream, the dissolved foreign
substance, for example the dissolved SO.sub.2, is transferred from
the solution into the gas stream and passed through a foreign
substance-sensitive sensor in which a concentration-dependent
signal is generated.
[0048] Quantitative release of the bound foreign substance, for
example the bound SO.sub.2 in a matrix, e.g., in wine, requires
drastic ambient conditions (high temperature, strong acid) or
requires a long time period to achieve chemical equilibrium. Since
the measurement is carried out according to an aspect of the
invention by a gas stream that is passed through the sample, the
quantitative conversion can proceed very rapidly.
[0049] The heating of the sample in the sample container can
preferably be carried out through the resulting hydration
energy/dilution heat that is released when concentrated acid comes
into contact with an aqueous medium. Advantageous here is the
elimination of mechanical and/or electrical components, as well as
the possibility of a common line route for reagents to detect
dissolved foreign substance (for example free SO.sub.2 at low
temperatures ("cold"), and total SO.sub.2, i.e., of the originally
dissolved and bound SO.sub.2 at elevated temperatures
("warm")).
[0050] The determination of the free SO.sub.2 (SO.sub.2 dissolved
in the matrix) is preferably carried out under mild conditions
where possible, so that the bound SO.sub.2 is not released by the
reagents, since this would distort the measurement. The reference
procedure provides for cooling of the reagent/matrix mixture to
preferably below 20.degree. C., most preferably to approximately
10.degree. C.
[0051] In the determination of the total content of dissolved and
bound SO.sub.2, the SO.sub.2 is preferably bound through the
addition of an adduct former in excess. Pyruvic acid or a salt
thereof can advantageously be used as adduct former. The salt has
the advantage that it is present in a solid state and in this form
is sufficiently chemically stable. The pyruvic acid has a
relatively high binding affinity and delivers stable bisulphite
adducts. It is preferably used in the form of a solution. This
solution lies pre-metered in the sample container. However, it can
also be added by the user through a dropping pipette.
[0052] For better mixing of the sample upon supply of the acid
reagent a sample container is preferably used which has, for
example, as substrate an agar layer, possibly mixed with some
pyruvic acid or a salt thereof, on its base. This layer liquefies
under the influence of acid/heat and ensures mixing of the solution
(for example wine as matrix). The pyruvic acid or the salt of
pyruvic acid is added to this agar layer as a solution or in solid
form and the sample is then added. If sulphuric acid
H.sub.2SO.sub.4 is added as reagent then this would sink downwards
because of its high density, whilst the sample, for example wine,
would float to the top because of its lower density. The
dissolution process of the substrate, however, brings about an
advantageous mixing, so that sample and acid are sufficiently in
contact, even at small sample volumes.
[0053] According to a further aspect of the invention a method is
proposed for the determination of a content of at least one foreign
substance in a matrix of a solid or liquid food, in which an
originally dissolved foreign substance is first bound in the
reaction area in the matrix, and foreign substance originally
dissolved in the matrix is released in a delayed manner such that
the originally dissolved foreign substance and any foreign
substance originally bound are released together from the matrix in
the same process step; and the determination of content of the
foreign substance released in the same process step is carried out
by a sensor.
[0054] An adduct former which binds the dissolved foreign substance
can advantageously be added to delay the release of the foreign
substance. A reagent can preferably be added for the release of the
foreign substance.
[0055] Furthermore, the adduct former can advantageously contain
pyruvic acid or a salt of pyruvic acid and the reagent can contain
sulphuric acid and/or phosphoric acid.
[0056] The matrix can preferably be a liquid and/or a solid food,
in particular wine or a wine constituent, fruit juices, beer, dried
fruit, in particular an extract from dried fruit and the foreign
substance can be SO.sub.2 that is bound in food and/or
dissolved.
[0057] Further, it is proposed to use one or more reagents and/or
one or more adduct formers that are suitable for implementing a
method for testing of solid and liquid foods, especially wine,
fruit juices, beer, dried fruit and the like for one or more
foreign substance contents.
BRIEF DESCRIPTION OF THE DRAWINGS
[0058] The invention is described in more detail below with
reference to the embodiments shown in the drawing. The Figures are
shown schematically
[0059] FIG. 1 A preferred measurement arrangement of a device
according to the invention;
[0060] FIG. 2 A perspective view of a preferred device according to
the invention;
[0061] FIG. 3 A reagent container inserted in a reagent area of the
device of FIG. 2, shown in detail;
[0062] FIG. 4 A sample holder connected to a reaction area shown in
detail;
[0063] FIGS. 5a, 5b A preferred sensor (FIG. 5a) and a reference
electrode (FIG. 5b) for the sensor;
[0064] FIG. 6a-6c A preferred ready-made sample container in
different stages of preparation for determination; and
[0065] FIG. 7 A flow chart of a preferred measurement process.
[0066] Same or equivalent-acting elements are assigned the same
reference numerals in the drawings.
DETAILED DESCRIPTION
[0067] FIG. 1 shows, for description of an aspect of the invention,
schematically the construction of a preferred device 100. A reagent
container 50 is connected via a transfer line 13 in flow connection
with a sample container 80. Downstream of the sample container 80 a
sensor area 90 is provided which is connected to the sample
container 80 via a line 15. An output line 17 leads outwards from
the sensor area 90. A pump 34 transfers a carrier medium through
the pump line 11 to the reagent area 40. The carrier medium is
preferably a gas, for example ambient air, which is expediently
drawn in through a filter 32. The carrier medium can also be taken
where appropriate from a gas cylinder. The pump 34 can be arranged
upstream of the reagent container 50 in the pump line 11 or
downstream of the reagent container 50, for example in the transfer
line 13.
[0068] A reagent 58, for example sulphuric acid (H.sub.2SO.sub.4),
can be specifically fed from the reagent container 50 to the sample
container 80, said reagent completely releasing the foreign
substance 89 contained in a matrix 88 in unbound form and possibly
in bound form. It is provided that a possibly unbound (dissolved)
foreign substance is fully bound in advance, in particular through
addition of an adduct former.
[0069] The reagent container 50 is attached to a needle system 48
which, for example, comprises two hollow needles 42 and 44. The
hollow needles 42, 44 of the needle system 48 preferably project
upwards and are parallel to each other. An embodiment, for example
with coaxial hollow needles or needles with an inner hose is also
possible. In a favourable further development, not shown, the
hollow needles 42, 44 may be integrated as a component in a carrier
body which has connections to the pump line 11 and to the transfer
line 13. The needle system 48 can then be easily replaced.
[0070] The carrier medium enters the reagent container 50 via the
hollow needle 42 on the inlet side. The reagent is withdrawn from
the reagent container 50 via the hollow needle 44 on the outlet
side and is fed to the sample container 80. A matrix 88 therein,
which contains the foreign substance 89 to be detected, such as
wine with a content of SO.sub.2, is mixed with the reagent 58 and
the content of foreign substance 89 is determined in the sensor
area 90. A sensor 92 is provided in the sensor area 90 for
determination. The foreign substance 89 is preferably passed in gas
form into the sensor area 90 and fed to the sensor 92. The foreign
substance 89 can also be fed to the sensor 92 as a solution where
appropriate.
[0071] The reagent container 50 is preferably a pre-filled, in
particular pre-dosed ampoule which the user simply inserts when
needed in the device 100 described in more detail below. The
reagent container 50 configured as a pre-dosed ampoule, contains
one or more reagents 58 suitable and/or necessary for the specific
detection of a foreign substance in exactly the dose that is
matched to the quantity of sample (matrix 88 with foreign substance
89). The reagent container 50 is advantageously configured, i.e.,
its dimensions are such, that it can be introduced into a
corresponding reagent area 40 (FIG. 2) that is configured in a
complementary manner of the device 100. Incorrect operation the
device 100 can thereby be avoided.
[0072] The reagent container 50 can be connected, for example in
the form of a pierceable ampoule with a pierceable septum, as
closure with a two needle system 48 of the device 100. The reagent
container 50 can also be an ampoule, a vial with snap-on lid, a
vial with crimp closure or the like.
[0073] The reagent container 50 is thereby attached to the needle
system 48 through its under-side. The "upside down" assembly of the
reagent container 50 enables it to be reliably emptied. An assembly
is also conceivable, however, in which the reagent container 50 is
connected to the reagent area 40 with the closure facing upwards or
to the side.
[0074] The carrier medium, for example air, which is later required
for measurement, transported by the pump 34, enters through the
hollow needle 42 on the inlet side shown on the left in the figure,
into the reagent container 50 in the form of an ampoule. Through
excess pressure, the reagent 58 is transferred through the right
hollow needle 44 on the outlet side into the further measurement
system of the device 100. By means of the following carrier medium
stream delivered by the pump 34, the foreign substance 89, for
example SO.sub.2, driven out of the matrix 88 by the reagent 58, is
fed from the sample container 80 to the sensor 92 of the sensor
area 90. The hollow needle 42 on the inlet side preferably extends
into the reagent container 50 to a lesser extent than the hollow
needle 44 on the outlet side, so that an excess pressure that may
already be present in the reagent container 50, or which is
generated upon piercing, is reduced through the hollow needle 44 on
the output side before the hollow needle 42 on the inlet side comes
into contact with the interior of the reagent container 50.
[0075] The enclosed volume of the reagent container 50 preferably
lies between 0.2 ml and 15 ml, preferably between 0.5 and 10 ml.
The enclosed volume of the reagent container 50 can be completely
or partially filled with the reagent 58, for example a liquid. The
reagent container 50 is preferably configured to hold a reagent
quantity for exactly one measurement. A new reagent container 50
can therefore be used for each measurement. The fill quantities of
reagent container 50 and sample container 80 are preferably matched
exactly to one another. With particular advantage, the sample
container 80 can already contain one or more specific chemicals in
exactly measured quantities for the detection of the foreign
substance 89. The reagent container 50 and the sample container 80
can preferably be made available as a detection-analysis set. The
user only has to add to the sample container 80 a predetermined
amount of the matrix 88, which contains the foreign substance 89.
The user can therefore always carry out the determination of
foreign substance content in the matrix 88 under precisely defined
conditions.
Even in cases where the reagent 58 exhibits corrosive behaviour
and/or is sensitive to air, moisture and/or other constituents of
the surrounding room air at the point of use for detection or
during transport and storage, stable measurement and certain
transfer to the sample container 80 are possible. Outside the
device 100, the reagent 58 in the reagent container 50 is tightly
sealed until use and only after the attachment of the reagent
container 50 to the needle system 48 as needed is it accessible.
Moreover, the quantity of the reagent 58 is limited to that
quantity required for detection and does not need to be metered by
the user.
[0076] In a preferred use of an aspect of the invention, SO.sub.2
is detected as a foreign substance 89 in wine as matrix 88. To
detect the total content of dissolved and bound foreign substance,
in particular SO.sub.2 in wine, H.sub.2SO.sub.4 is preferably used
as the reagent 58, in a concentration such that after mixing of the
reagent 58 with the sample (including additions such as adduct
former etc.) the acid concentration is preferably 15%-85%,
preferably 40%-85%. Other organic or inorganic acids, for example
phosphoric acid, can favourably be used in comparable concentration
ranges.
The needle system 48, as well as the following downstream line 13
are preferably protected against corrosion. Stainless steel
capillaries of stainless steel types that are available
commercially can favourably be used for the needle system 48 and/or
the line 13 and for the other lines 11, 15 and 17, for example
stainless steels 1.4401, 1.4571, 1.4541, 1.4301, 1.4404, or alloys,
in particular alloys containing Cr, Mo, Ni. It is also conceivable
to use other materials such as precious metals, glass, ceramics,
plastics.
[0077] Stainless steel can normally be severely attacked by the
reagent 58 used, which contains, for example, semi-concentrated
sulphuric acid, if it is in contact with it for a longer period. In
accordance with an advantageous further development of an aspect of
the invention, the reagent 58 is therefore mixed with an inhibitor
that reduces or completely prevents corrosion. For the detection of
SO.sub.2, for example, a 40%-85% sulphuric acid is modified through
the addition of one or more inhibitors, such as iron (III) salts,
such that there is no longer an attack on the stainless steel
capillary. The inhibitor is expediently added to the reagent 58 and
can expediently be already contained in the pre-filled reagent
container 50.
[0078] If different reagents 58 are used in the device 100
according to an aspect of the invention, for instance to detect the
presence of a foreign substance 89 in the matrix 88 by different
methods, then a suitable inhibitor is expediently added to all
corresponding reagents 58, which are used in a reagent container
50, to maintain a defined inhibitor concentration. Such a case can
occur, for example, when the device 100 contains "free" foreign
substance 89, i.e., that is not bound in matrix 88, but instead is
in solution and two different methods are to be used to detect the
total content of foreign substance, namely free foreign substance
and bound foreign substance in the matrix 88. For the determination
of free and total foreign substance content, for example, two
different reagents 58 are used in the same system, to which, for
example, an appropriate amount of inhibitor, such as iron (III)
salts, has been added.
[0079] If the inhibitor concentration is markedly reduced compared
to the reagent 58, for example through inadequate rinsing of the
capillary with pure water, then corrosion phenomena can occur. It
is therefore recommended that the capillaries be rinsed
sufficiently with pure water or other suitable rinsing solutions.
Rinsing with an aqueous solution of the inhibitor can be
advantageously carried out. This may be additionally, or
alternatively, to the fact that the reagent 58 is mixed with the
inhibitor.
[0080] After connecting the reagent container 50, the reagent 58
may be completely transferred through the transfer medium pumped by
the pump 34 from the reagent container 50 into the sample container
80.
[0081] The sample container 80 is preferably configured so that it
can be connected to a suitable reaction area 60 of the device 100.
For this the reaction area 60 can have a cone-shaped coupling 72,
that can have a sealing ring on its outer circumference, over which
the, for example cylindrical, sample container is pushed. Instead
of a sealing ring a press fit or other suitable sealing means can
also be provided. The coupling 72 can be recognised in the recess
70 in the detail view of FIG. 3.
[0082] The sample container 80 preferably has dimensions such that
when it is full exactly one measurement can be carried out for the
detection of a foreign substance 89 in a matrix 88 with matched
volumes of matrix 88 and an adduct former 84. The addition of
adduct former 84 allows the simultaneous determination of the
content of dissolved and bound foreign substance, especially of
SO.sub.2. The adduct former 84 is preferably contained in the
pre-filled sample container 80 and does not need to be supplied by
the user. Alternatively, the adduct former 84 can be separately
provided to the user in a suitable dosage in the preferred
detection analysis set and fed only at the time of measurement.
[0083] The reaction area 60 preferably comprises a connection
system 62 with a first connection 64 on the inlet side through
which the reagent 58 can be fed, and a second connection 66 on the
outlet side, through which the foreign substance 89 can be passed
to the sensor area 90. The connections 64 and 66 project out of the
conical coupling, wherein at least one of the connections 64 passes
through a stopper 68 (FIG. 4) that serves as a splash guard for the
sample container 80. The connections 64, 66 can be formed as hollow
needles, or be formed as hoses or small tubes. A coaxial embodiment
with hollow needles that extend inside one another and/or hoses
and/or small tubes is also possible.
[0084] If the sample container 80 is attached with its opening open
in an upward direction to the coupling of the reaction area 60,
then the connection 64 on the inlet side, which feeds the reagent
58, preferably extends deeper into the sample container 80 than the
connection 66 on the outlet side, through which the foreign
substance 89 to be detected or a reaction product thereof is fed
out of the sample container 80 to the sensor area 90. The
connection 64 extends in particular into a mixing area, in which
the matrix 88, foreign substance 89 and, for detection of the total
content of SO.sub.2, the adduct former 84 are mixed, so that the
reagent 58 from the connection 64 can come into intimate contact
with the foreign substance 89 bound and/or free in the matrix 88.
The foreign substance is released by action of the reagent 58 into
the headspace 86 above the mixing area and can exit from the sample
container 60 in the direction of the sensor area 90 through the
connection 66 on the outlet side, which projects into the headspace
86.
[0085] For the detection of foreign substance 89 it can be
favourable to maintain the sample container 80 at a desired
temperature or within a desired temperature range. The sample
container 80 can where necessary be heated or cooled, depending on
the reaction that is being carried out in the sample container 80
at the time. Further details of the detection sequence are
described with reference to FIGS. 6 and 7.
[0086] The foreign substance 89 released from the matrix 88 through
the reagent 58 enters the sensor area 90 via the connection 66. The
sensor area 90 preferably has an electrochemical sensor 92, which
is explained in detail by reference to FIGS. 5a and 5b.
[0087] FIG. 2 shows, by way of example, a possible embodiment of a
preferred device 100 for detecting a foreign substance in a matrix
in accordance with the basic arrangement shown in FIG. 1. To avoid
unnecessary repetition, reference is made to the components
described therein, if they are not further explained here.
[0088] The device 100 is arranged in a housing 10 which houses a
control part 20, a reagent area 40 with a receptacle 41, for
example arranged as a depression, for the reagent container 50 and
an analysis part 30 with the reaction area 60 for the sample
container 80 and the sensor area 90. A line system comprising a
pump line 11 and a transfer line 13 (FIG. 1) serve for transfer of
the reagent 58 (FIG. 1) from the reagent container 50 into the
sample container 80. The carrier medium stream can also be produced
by a separate pump or a pressurized storage vessel and dosing be
provided as a separate unit. Instead of the receptacle 41 for the
reagent container 50, a metering pump and a reservoir
vessel/another metering unit could be used, in principle, to feed
the reagent 58.
[0089] The control part 20 comprises, for example, a keyboard 22, a
display 24, a start button 26 and a corresponding processing unit
(not shown) for control and if necessary for evaluation of the
measurement and for monitoring of the device 100.
[0090] The device 100 is very compact and allows secure handling of
reagent container 50 and sample container 80 with quantities and
volumes of the chemical components used that are exactly matched to
one another. The reagent container 50 can be used without risk of
mix-up, and the device 100 in the reagent area 40 can have a sensor
device 55, for example a light barrier 57, 59, a mechanical switch
or the like, which can establish the presence of the reagent
container 50. For this, the reagent container 50 can have
reflective markings 52, through which the device can recognise the
reagent container 50 used. Furthermore, as a simple coding this can
enable recognition of reagent containers 50 for different reagents.
However, other codings, for example bar code, mechanical coding,
etc., can be used so that the device can reliably prevent
measurements being carried out using reagents and samples not
intended for one another. Operational reliability is thereby
increased further, even with inexperienced users:
[0091] The receptacle 41 in the reagent area 40 is preferably
formed as a depression into which the reagent container 50 can dip.
The reagent container 50 can favourably be inserted into an insert
45 for this purpose. The reagent container 50 can preferably hold a
volume between 0.2 ml and 15 ml, preferably between 0.5 ml and 10
ml, of the reagent 58.
[0092] A preferred embodiment of the reagent container 50 has a
cylindrical cross section with a constriction 54 at one end, to
which a closure 56, such as a pierceable septum, is connected. The
insert 45 partially envelops the reagent container 50 through its
body 46, wherein a region for recognition of the markings 52
remains free, and engages in the constriction 54 such that the
reagent container 50 with the carrier 45 can be pressed into the
receptacle 41 of the reagent area 40 in the form of a recess, to
introduce the needle system 48 (FIG. 1) into the reagent container
50. The insert 45 has a retaining knob 47 at its upper end which
projects out of the recess 41 upon attachment of the reagent
container 50. This allows the reagent container 50 to be easily
removed again from the device 100 after the measurement. The
receptacle 60 is disposed in a recess 70 in which the sample
container 80 is inserted and over which a cone of the reaction area
60 can be pushed, through which the connection system 62, for
example a needle system, is accessible. A sensor can be arranged in
the recess 70, for example a photocell, a micro-switch or the like,
which recognizes the presence of the sample container 80 and passes
this on to the control system of the device 100. If the sample
container 80 is not inserted then the measurement cannot be
started.
[0093] FIG. 3 shows the reagent area 40 of the device 100 of FIG. 2
with a reagent container 50 inserted in the recess 41 in a
partly-exploded view. The reagent container 50 is attached with its
closure 56 facing downwards to the needle system 48 with the hollow
needles 42 and 44, as described in FIG. 1. The insert 45, which
envelops the reagent container 50 is not shown for clarity reasons.
A sensor 55, for example a light barrier with two transmitting and
receiving units 57, 59, is arranged next to the reagent container
50 and detects the presence of the reagent container 50, for
exampling through reflective markings 52 on the reagent container
50. If the reagent container 50 is not inserted, then the
measurement cannot be started. A cone-shaped coupling 72 is
recognisable in outline in an adjacent recess 70, onto which the
sample container can be pushed (not shown).
[0094] FIG. 4 shows how the preferred sample container 80 can be
connected to the reaction area 60. The reaction area 60 comprises a
feed system 62 configured by way of example as a needle system,
with a connection 64 on the inlet side configured as a hollow
needle, through which the reagent 58 (FIG. 1) is fed and a
connection 66 on the outlet side configured as a hollow needle,
with which the carrier gas containing the foreign substance 89 is
removed from the sample container 80. The feed system penetrates
through a stopper 68 which serves as splash protection. The
connection 64 on the inlet side as a hollow needle extends into a
mixing area 82, in which the matrix 88, foreign substance 89 and an
adduct former 84 are mixed, so that the reagent 58 from the
connection 64, configured as a hollow needle, comes into intimate
contact with the bound and/or free foreign substance 89 in the
matrix 88. The connection 66 on the outlet side configured as a
hollow needle projects into the headspace 86 above the mixing area
82. The connection 66 can end below or above the stopper 68 since
this does not seal the sample container 80 in a gas-tight
manner.
[0095] In an alternative arrangement the sensor 92 can be arranged
in this headspace 86, instead of in a remotely-located sensor area
90. It is also conceivable to have an immersion sensor with a
gas-permeable membrane that is immersed directly in the mixing area
82.
[0096] FIG. 5a shows schematically a three-electrode system with a
reference electrode 93 as preferred electrochemical sensor 92,
which is shown in detail in FIG. 5b. The reference electrode 93
serves as a potential reference point for the electrochemical
measurement, which can be carried out either potentiostatically or
galvanostatically.
[0097] The sensor 92 should preferably be operated with a
chloride-free reference electrode 93. The possibilities afforded by
such a usage, which is to be available with little effort and for
relatively inexperienced users, are severely limited. An
advantageous solution that is favourable in terms of environmental
technology is a lead/lead sulphate electrode (Pb/PbSO.sub.4),
which, however, is described in the literature as only
conditionally stable and therefore is regarded in practice as not
usable.
[0098] This can, however, contrary to general opinion, be
continuously regenerated in accordance with an aspect of the
invention through a preferred electrochemical treatment so that a
potential can be obtained that is sufficiently stable for the
duration of analysis. Before each analysis, and in between each
analysis, the reference electrode 93 is therefore preferably
regenerated and then offers a stable potential for about 5 minutes.
This period is entirely sufficient for a measurement procedure. The
value holds for a so-'called micro-electrode. Increasing the
surface area enables this time to be extended accordingly.
[0099] The advantage of the regenerative system, especially the
Pb/PbSO.sub.4 system, is evident in several aspects. The system of
reference electrode 93 is chloride-free, the long-term stability of
the system is more than a year in installed condition. Simple and
non-critical handling is possible, and the reference electrode 93
is stable in an acidic environment. There is no "bleeding" of the
system through differences in concentration, and there are no
disturbances or poisoning of the working electrode 96
(SO.sub.2-sensitive).
[0100] The reference electrode 93 has the theoretically-calculated
potential directly after manufacture. After installation there is
usually a marked drift, which can lead to a deviation of several
hundred mV. As a result, this electrode would not be useful for
analytical systems, where the maximum permitted deviation is just a
few mV. According to the preferred electrochemical treatment
according to an aspect of the invention, however, the reference
electrode 93 can be regenerated in a few seconds before each
measurement to exactly the starting potential.
[0101] A preferred electrochemical treatment can be carried out by
applying an electrical voltage to the reference electrode 93, which
enables current to flow. Typically, the potential of the reference
electrode at the time of the regeneration process is approximately
-1.5 to -3 volts relative to the counter electrode. The
counter-electrode 94 in the electrochemical sensor 92 is therein
used as a counter pole.
[0102] The working electrode 96 of the electrochemical sensor 92 is
disposed on a porous membrane 91 and comes in contact with a
carrier gas flowing past it, for example air, that is mixed with
the foreign substance 89, for example SO.sub.2 mixed with air,
through the line 15 from the sample container 80 (FIG. 4). The
carrier gas stream is indicated by arrows and is led away through
line 15c from the membrane 91. The reference electrode 93, together
with the auxiliary electrode 94, for example a gold wire, is housed
within the sensor housing 97 in a conductive liquid. Preferably,
the liquid contains sulphate ions (SO.sub.4.sup.2-) the liquid is
in particular preferably H.sub.2SO.sub.4.
[0103] To avoid drying out of the membrane 91, a large proportion
of the carrier gas stream is routed past the membrane 91. To this
end, the line 15 splits into a very narrow branch 15a, which is
much narrower than the line 15, and into a wide branch 15b, which
is much wider than the branch 15a. The branches 15b and 15c open
separately into the line 17, through which the carrier gas stream
can leave the sensor 92, but may also be merged beforehand.
Alternatively, they can also be routed individually outwards.
[0104] In addition to a possible drying-out of the membrane 91,
preferably a Teflon membrane, and/or the working electrode 96,
which can be deposited as a layer on the membrane 91, splitting of
the carrier gas stream in the branches 15c and 15b enables
avoidance of a sensor signal that is too large, and allows
compensation for fluctuations in the gas flow. This splitting can
optionally also be designed to be switchable, so that the entire
carrier gas stream with the foreign substance 89 flows via the
sensor 93. Alternatively, the splitting can be replaced by a less
gas-permeable sensor membrane.
[0105] In a preferred rinsing cycle to clean the sensor area 90/the
sensor 92, the splitting process is switched off for about 95% of
the rinsing time by closing the branch 15b, so that an increased
rinsing action can be achieved.
[0106] The sensor 92 can be rinsed regularly with a moist medium to
supply the membrane 91 with sufficient moisture.
[0107] The reference electrode 93 preferably comprises a
Pb/PbSO.sub.4 system and can have, as shown in FIG. 5b, a Pb
inclusion 93a at the head end of a tube 95, for example a glass
tube, which projects outwards with a Pb surface 93b. The Pb
inclusion 93a seals the inside of the tube 95 against penetrating
liquid. The bond wire 95a serves for electrical contact to the Pb
inclusion 93a in the regeneration of the reference electrode
93.
[0108] If the reference electrode 93 is formed from a lead/lead
sulphate system (Pb/Pb.sub.nX.sub.m system), then the reference
electrode 93 can be regenerated in its properties through an
electrochemically-induced reaction. Upon contact with the
conductive liquid the sulphate PbSO.sub.4 is formed from the
metallic Pb and upon regeneration metallic Pb is formed from
PbSO.sub.4. X preferably represents a particular ionic species in
the conductive liquid. In particular, the Pb/Pb.sub.nX.sub.m system
is a Pb/PbSO.sub.4 system with n=1, m=1 and X=SO.sub.4.sup.2-. The
electrochemically active materials in a Pb/PbSO.sub.4 system are Pb
and Pb (II) sulphate and/or Pb and Pb (IV) sulphate. A reference
electrode 93 in which SO.sub.4.sup.2'' is replaced by PbO is also
conceivable.
[0109] In principle, such a reference electrode 93 in the form of
reference electrode 93 can also be used in other sensors, such as
biosensors, chemical sensors or the like in which a chloride-free
reference electrode system is desired. An improvement in stability
can be achieved through the use of alloys instead of a pure metal,
as for example here Pb.
[0110] Instead of an electrochemical sensor 92 another method with
a different sensor type can naturally also be used and, for
instance, a photometric determination of the foreign substance 89
can be carried out. The electrochemical sensor 92 is therein
replaced, for example, by a photometric detector unit (not shown).
In the case of detection of SO.sub.2 in wine, by way of example, an
indicator solution (pararosaniline formaldehyde mixture/DTNB) or
sulphite oxidase and NADH can be introduced into the sample
container 80, and the blank value determined photometrically.
SO.sub.2 is then released as described later, wherein a reaction
(colour reaction or consumption of NADH) takes place, which can be
detected and quantified photometrically. For coloured samples, it
may be favourable to add the indicator solution or to run the
enzymatic determination not in the sample, but by separating the
sample and the indicator through a semi-permeable membrane, a gas
stream or the like. With less coloured samples determination can be
carried out directly in the sample.
[0111] The released SO.sub.2 is combined with the pararosaniline
formaldehyde mixture, and a colour reaction is seen after a
corresponding waiting period. A photometric unit can be used to
measure and quantify the absorption change at a specific
wavelength. Another possibility is a colour reaction with DTNB
(5,5'-dithio-bis(2-nitrobenzoic acid)). In the presence of sulphite
DTNB is cleaved to TNB (2-nitro-5-mercaptobenzoic acid), which
causes an intense yellow coloration, which can be quantified
photometrically. Similarly, an enzymatic detection can be used.
Sulphite oxidase is used in the enzymatic detection. In the
presence of oxygen and water, sulphate and hydrogen peroxide are
formed from sulphite, which in turn reacts with NADH
(nicontinamide-adenine dinucleotide). The quantitative
determination is carried out photometrically via the consumption of
NADH. The detector unit can thereby be separated from the sample
through a membrane or a gas line system.
[0112] FIGS. 6a-6c illustrate the preparation of a preferred sample
container 80 for determining the content of a foreign substance 89
in a matrix 88, in particular a determination of SO.sub.2 content
in wine, in particular the entire content of dissolved and bound
SO.sub.2.
[0113] In accordance with a preferred embodiment, the pre-filled
sample container 80 is filled with a substrate 83 that is stored in
the bottom area of the sample container 80 (FIG. 6a), which later
forms a mixing area 82. The substrate 83 is, for example, a gel,
gelatine, agar-agar or the like, which dissolves upon contact with
water, causing vortexing of the solution and thus good mixing of
the components coming into contact therewith, even with relatively
small sample volumes. An adduct former 84 is preferably added to
the substrate 83. It is not necessary to use the substrate 83.
[0114] An adduct former is added to bind the content of dissolved
foreign substance 89. The adduct former 84 is a binding partner for
the dissolved foreign substance 89. Preferably, the entire "free",
i.e., dissolved foreign substance 89 is bound to the binding
partner, through which the release of foreign substance 89 from the
matrix 88 is influenced, in particular, is delayed. The release
characteristics for the originally dissolved and originally bound
foreign substance 89 are equalised. An acidic pH is preferably set
for the release of the foreign substance 89.
[0115] In the determination of SO.sub.2 in wine, a binding partner
that has at least one aldehyde and/or ketonic group, enabled for
bisulphite addition is preferably added immediately before the
measurement to bind the remaining free SO.sub.2 and to equalise the
concentration and/or time profiles. This is done preferably when
the total content of foreign substance 89 in dissolved and bound
form is to be determined. If only the content of dissolved foreign
substance 89 is to be determined, then addition of the adduct
former 84 can be omitted.
[0116] The adduct former 84 can be added in solid form or in liquid
form as a pure substance or solution. Advantageously, the adduct
former 84 can be dosed as a solution in sample vials or
freeze-dried and can therefore be transferred into a transportable
state. An amount of adduct former 84 can be provided in sample
containers 80 in ready-to-use form for the user that is matched
exactly to the quantity of matrix 88 containing foreign substance
89 that is to be added.
[0117] Alternatively, for delayed release of the dissolved content
of foreign substance a covering through a barrier layer is also
conceivable, for example a floating layer with a lower specific
density than water, for example an oil layer, which prevents
premature release of the dissolved foreign substance 89. To avoid
strong foam formation a defoamer may be added, such as a silicone
oil-containing agent. Similarly, a delay of the foreign substance
transfer can also be enabled through the formation of polymer in
the sample, through addition of a polymer-forming component which
polymerises preferably under acid influence. It is also conceivable
to pass the carrier gas not through the matrix 88, but to arrange a
permeable layer between the carrier gas and the matrix 88, which
separates the carrier gas from the matrix 88 and permits the
passage of the foreign substance 89 from the matrix 88 into the
carrier gas in the headspace 86.
[0118] As indicated in FIG. 6a, a defined quantity of the matrix 88
under investigation, which possibly contains foreign substance 89,
is added, for example using a pipette (FIG. 6b). The amounts of
adduct former 84 and matrix 88 are advantageously matched to one
another. The adduct former 84 is present in excess compared to the
expected amount of foreign substance 89.
[0119] The matrix 88 containing the foreign substance 89 mixes with
any substrate 83 present and the adduct former 84 (FIG. 6b),
wherein the substrate 83 is dissolved and the foreign
substance-containing matrix 88 and adduct former 84 are mixed. In
accordance with an aspect of the invention the adduct former 84
first brings about binding of the free fraction of the foreign
substance 89, which is dissolved in the matrix 88 (FIG. 6b). The
originally free fraction of the foreign substance 89 is then in
bound form and can be released together with fraction of the
foreign substance 89 originally bound in the matrix as soon as the
matrix 88 comes into contact with the reagent 58 (FIG. 6c).
[0120] The addition of the reagent 58 causes cleavage of the bonds,
as a result of which the total content of foreign substance 89,
i.e., the content originally dissolved in the matrix 88 and the
content originally bound in the matrix 88, is released and can be
transported out of the headspace 86 through a carrier gas to the
sensor area 90. The delayed release of the originally dissolved
content of the foreign substance 89 at the same time as the
originally bound content of the foreign substance 89 enables
measurement of the total content of foreign substance 89 in the
matrix 88 with sufficient accuracy. Different concentration
profiles for foreign substances 89 that are bound to differing
degrees because of the measurement of foreign substance content not
in chemical equilibrium can be advantageously avoided.
[0121] Thus, in the detection of SO.sub.2 in wine, different
concentration profiles of the sulphite-containing species, bound to
differing degrees, are to be expected. Without the preferred
measurement sequence according to an aspect of the invention, an
early rise in the concentration of the sulphite, present as free
SO.sub.2, would be observed, which would then fall relatively
steeply after reaching the maximum concentration. For species for
which the chemical equilibrium lies strongly on the side of the
bound sulphite, concentration curves can be seen that only reach a
maximum value late on and then fall relatively slowly. In
accordance with an aspect of the invention in the presence of very
different species in unknown concentrations an equalisation of the
concentration profile can be carried out for simple mathematical
determination of the concentration via the sum of all sulphite
species.
[0122] The use of a strong acid as a reagent 58, preferably at
least half-concentrated sulphuric acid, is favourable for
determination of foreign substance content for release of the bound
foreign substance 89.
[0123] For this, the sample container 80 can be adjusted to a
suitable temperature. A heating and/or cooling system can be
provided (not shown) with a heating device and/or a cooling device
as well as one or a plurality of suitable mounted temperature
sensors. Alternatively or additionally, a substance can be added to
the sample container which does not disturb the reaction, but
which, however, has a suitable positive or negative enthalpy of
solution. Negative enthalpy of solution means that when the
substance is dissolved in a solvent, for example water, heat is
released and positive enthalpy of solution means that the substance
absorbs heat when it is dissolved. Thus the content of the sample
container 80 can be selectively heated or selectively cooled
without the need to provide additional mechanical or electrical
components. The solvent can be advantageously contained in the
reagent 58 and/or in the matrix 88.
[0124] For heating, the hydration energy of an acid can, for
example, be specifically used, and it can be added, for example, as
reagent 58. This allows the hydration energy of H.sub.2SO.sub.4 as
reagent 58 to be advantageously exploited for the release of the
SO.sub.2. The H.sub.2SO.sub.4 is preferably used at least
half-concentrated. This is particularly advantageous if the
detection is to be carried out not only for dissolved, but also for
the bound foreign substance 89.
[0125] Ammonium sulphate can advantageously be added for cooling as
it withdraws heat when it is dissolved. This is advantageous if
only the content of the foreign substance 89 dissolved in the
matrix 88 is to be determined, but not the content of bound foreign
substance 89. Detection of the dissolved foreign substance 89 in
the matrix 88 is carried out under milder conditions than those for
detection of foreign substance 89 bound in the matrix 88.
[0126] In addition to the elimination of the need for mechanical
and/or electrical components as compared with known devices it is
possible with the method according to an aspect of the invention to
use a common line route for reagents that allow free or bound
foreign substance 89 to be determined.
[0127] Heating of the sample container 80 is preferably carried out
when the total content of foreign substance 89 in dissolved and
bound form is to be determined. If only the content of dissolved
foreign substance 89 is to be determined, then cooling of the
sample container 80 is preferred.
[0128] A preferred procedure for measurement is described in more
detail in FIG. 7 based on a determination of a sulphite content
(SO.sub.2, foreign substance 89) in wine (matrix 88).
[0129] The foreign substance content in the matrix to be
investigated, for example a wine sample, can vary widely. A
fraction may be present as free SO.sub.2, which is dissolved in the
wine matrix. A significant fraction, however, is bound to various
components in wine (bisulphite addition to, for example, aldehyde
or ketonic groups). Different components bind the SO.sub.2 to
varying degrees.
[0130] Digestion of the bound SO.sub.2 is by means of a
non-volatile acid. Phosphoric acid or sulphuric acid, for example,
are favourable. The heat generation upon dilution is much more
pronounced for sulphuric acid so that it alone can bring about
complete conversion of the bisulphite adducts without any
additional heat source. For example, an approximately 80% sulphuric
acid can be used. For example, 1.5 ml acid can be added to 0.2 ml
sample. Preferably, the acid is contained in a reagent container 50
in the form of a pre-dosed ampoule with pierceable septum, to avoid
expensive dosing systems.
[0131] The corrosive action of sulphuric acid on most commonly-used
stainless steels is disadvantageous, so that either inert materials
are preferred for the line system in the device 100 and/or the
corrosive action of acid is reduced by suitable additives. This is
favourably achieved, for example, by the addition of iron salts to
the acid. The choice of material is severely limited by the
technical arrangement of reagent feed (e.g., pierceable ampoule) as
this requires an adequate stability.
[0132] The free SO.sub.2 in the wine, however, is determined under
"mild" reaction conditions. The existing bisulphite adducts should
not thereby be adversely affected. An acidic environment is
required to drive the SO.sub.2 out of the solution. A non-volatile
acid is preferably used as acid (for example phosphoric acid). The
reaction conditions can be optimized further by cooling the system,
for example, by the addition of salts with a positive enthalpy of
solution, which cause a cooling upon dissolution, or an active
cooling through a suitable cooling element.
[0133] The measurement routine commences at step 200. In step 202
it is established whether the sample container 80 has been placed
in the reaction area 60 and the corresponding reagent container 50
in the reagent area 40 and the device 100 (FIG. 1). The reagent
container 50 is advantageously filled ready for use with the
reagent 58 and only has to be placed by the user in the reagent
area 40. The sample container 80 is preferably filled ready for use
as necessary and is provided by the user shortly before the start
of measurement with a defined amount of a wine sample to be
investigated. By appropriate coding on the reagent container 50
and/or the sample container 80 it can be determined whether the
reagent container 50 containing the correct reagent 58 is available
for the test sample in the sample container 80.
[0134] If the reagent container 50 and/or the sample container 80
are not at the intended place in the device 100, or a false reagent
container 50 has been inserted then the measurement routine cannot
be started and it ends at step 238. Optionally, an alarm signal is
issued and the malfunction is displayed to the user. The
measurement routine can be started, for example, through a start
signal by pressing a button, keyboard input, input via touch screen
or the like. The start signal may be triggered before or after
adjusting the reagent container 50 and the sample container 80.
[0135] If the reagent container 50 and the sample container 80 are
correctly placed in the device 100, it is established in step 204,
in which mode measurement is to be carried out, i.e., if only the
free SO.sub.2, is to be determined or if the total amount of free
and bound SO.sub.2 is to be determined in the wine.
[0136] If "total SO.sub.2" is to be measured then an adduct former
84 is contained in the ready to use pre-filled sample container 80.
This can be provided ready for use, with or without substrate 83,
in the sample container 80 before the wine sample to be tested is
added. Shortly before the start of measurement a wine sample is
added in a defined amount to the sample container 80. During a
short reaction time of, for example, 0.5-2 minutes, the free
SO.sub.2 contained in the wine is bound by the adduct former 84,
for example a sodium salt of
pyruvic acid. The SO.sub.2 fractions in the wine sample are now
present only in bound form.
[0137] After sufficient reaction time, in step 222 the reagent 58,
preferably H.sub.2SO.sub.4, is introduced into the sample container
80, whereby a carrier agent, for example the pump 34, pumps a
carrier gas into the reagent container 50 and the reagent 58 is
forced out of the reagent container 50 into the sample container
80.
[0138] After a reaction time of, for example, 1 minute, during
which the SO.sub.2 adducts are split into the educt SO.sub.2 and
adduct former 84, the released SO.sub.2, which now contains both
the originally dissolved and bound fractions, is driven out of the
sample container 80 by a carrier gas stream, for example air,
delivered by the pump 34 and is fed to the sensor area 90 (FIG. 2).
A salt of pyruvic acid is preferably used as adduct former 84, and
has the advantage that it is present in solid state and in this
form is sufficiently chemically stable. The pyruvic acid has a
relatively high binding affinity and delivers stable bisulphite
adducts. The adduct former 84 can be added as a tablet or in liquid
form as solution or liquid to the wine or be already contained in
the sample container 80 in the desired quantity.
[0139] The data is evaluated in step 230, and is represented
visually in a display in step 232, for example optically, with
output of a measurement record in step 234.
[0140] If only the amount of free SO.sub.2 is to be measured then
the first reaction period in which the free SO.sub.2 is to be bound
is eliminated since no adduct former 84 was introduced into the
sample container 80/a pre-prepared sample container was used
without adduct former 84. Step 204 is therefore followed by step
210 in which the reagent 58 is transferred to the sample container
80. In step 212, a carrier gas stream flowing through the reaction
mixture drives the SO.sub.2 out and transports it to the sensor
unit 90. The detection of free (dissolved) SO.sub.2 requires only
relatively mild reaction conditions. If necessary, the sample
container 80 can be cooled to avoid an unwanted release of the
bound SO.sub.2 fraction in the wine sample because of an
undesirable rising temperature.
[0141] The data is evaluated in step 230, and can be represented
visually in a display in step 232, with output of a measurement
record in step 234.
[0142] The analysis can theoretically be carried out in a number of
ways: [0143] Numerical integration of the measurement curve (area
of the curve) [0144] Average value over a certain range [0145]
Median over a certain range [0146] Peak height [0147] Optional
baseline correction [0148] Evaluation of the complete measurement
curve up to a certain residual SO.sub.2 content in the carrier gas
[0149] Evaluation of only parts of the measurement curve (time
sections or dependence on signal levels/relative signal levels)
[0150] Evaluation of the signal plateau of the measurement curve
(for example with a gas circulation in which the gas transported
out of the sample container 80 is circulated to the sensor 92 and
via the reagent container 50 back to the sample container 80 and
sensor 92).
[0151] At the end of data evaluation the sample container 80 is
removed from the device 100 and the sample head cleaned, for
example, wiped with a damp cloth. A rinse vial can be inserted
instead of the sample container 80, whereby the rinsing process is
started automatically in step 236 and lasts, for example, 1 minute
and the measurement routine ends in step 238. The rinse vial is
then removed and the sample head wiped dry. The empty reagent
container 50 is removed from the device.
[0152] Favourable parameters for the measurement are given by way
of example below. Possible acids for the determination of SO.sub.2
are sulphuric acid, phosphoric acid, hydrochloric acid as well as
any organic or inorganic acids, which allow a suitable pH to be
achieved. Acids which are not volatile, or have only a low
volatility or if they are volatile do not interfere with the
detection of SO.sub.2 in the concentration range and temperature
range used are preferably suitable.
[0153] A favourable pH range according to an aspect of the
invention for the determination of total SO.sub.2 content, i.e.,
the content of dissolved ("free") and bound SO.sub.2 is pH<1 for
the solution, which is present in the sample container 80 after
addition of the reagent 58. This can be achieved, for example,
through approximately 0.1 mole/L sulphuric acid in this solution,
or through approximately eight percent phosphoric acid in this
solution, depending on the chemical composition of the
solution.
[0154] The higher the degree to which the pH value is lowered,
i.e., the higher the acid concentration in the solution, the more
readily the bound SO.sub.2 is converted into dissolved
SO.sub.2.
[0155] A favourable pH range for the determination of the content
of free SO.sub.2 is between 0.5 and 2, preferably between 0.8 and
1.5 for the solution which is present in the sample container 80
after the supply of reagent 58. This corresponds roughly to a
concentration of 0.03-to 0.2 moles/L sulphuric acid in this
solution. Accordingly, phosphoric acid can also be used in
appropriate concentration.
[0156] The protolysis range of sulphurous acid is known to be such
that at low pH values (for example pH=0) and high pH values (for
example pH=10), the SO.sub.2 is present almost entirely in the free
form. To ensure complete release of the bound SO.sub.2, the entire
SO.sub.2 should therefore be determined in the highly acidic
region. Alternatively, determination is also possible in the highly
alkaline range.
[0157] To obtain the molecular SO.sub.2 present in the solution,
the pH value should be below approximately pH=1.5, since only this
form can be converted into the gas phase. To determine the content
of dissolved SO.sub.2 under these conditions it is necessary to
counteract conversion of bound SO.sub.2. For this a low temperature
is preferably chosen to avoid a back-reaction of bisulphite
adducts. This also makes it possible to use low pH ranges,
preferably below pH=1.5, to obtain a presence of molecular SO.sub.2
in the solution. A temperature between 0.degree. C. and 25.degree.
C. is therefore suitable for determination of the content of
dissolved SO.sub.2.
To determine the total content of SO.sub.2 in the wine matrix, the
pH should be as low as possible. This firstly has a favourable
effect on the presence of molecular SO.sub.2 and secondly enables a
back-reaction of the bisulphite addition. The pH value should be
less than pH 1, and be preferably <0.5 for the detection of the
bound SO.sub.2. An elevated temperature can accelerate the
back-reaction. Elevated temperatures and a strongly acidic
environment are therefore favourable for the determination of the
total content of SO.sub.2.
[0158] Some preferred reagent compositions and quantities are given
below. The percentages refer to percent by weight.
[0159] 1) Determination of the Total Content of SO.sub.2 in
Wine:
Sample volume of wine in the sample container 80, for example
100-300 .mu.l, preferably 150-250 .mu.l.
[0160] Component 1: Adduct former (10-100 .mu.l, preferably 20-50
.mu.l per sample)
Concentrated solution of sodium salt of pyruvic acid in water. A
concentrated solution is favourable, since this takes up only a
small volume. However, a more dilute solution can also be used.
[0161] Component 2: agar layer (100-400 .mu.l, preferably 150-250
.mu.l per sample)
0.3-2.5%, preferably 0.5-1.5% agar (solution of 0.3-2.5 g,
preferably 0.5-1.5 g agar in 100 ml water) 5% sodium salt of
pyruvic acid
[0162] Less than 0.3% agar leads to gels of low stability, too high
a concentration leads to solid gels, which are less suitable.
Preferred is a range of 0.3 to 2.5%. The pyruvic acid or salt
thereof can optionally also be omitted, since the adduct former
(component 1) is added and this addition cannot be replaced by the
content in the gel.
[0163] Component 3: Acid (1-3 ml, preferably 1.25-1.75
ml/sample)
70-90% sulphuric acid with approx. 0.2 to 5%, preferably 1-1.5% Fe
(III) sulphate hydrate. Acid concentrations that are too high
present technical difficulties and can also influence the
constituents of the wine in a disruptive manner. Concentrations
below 60% require additional heating. With additional heating
approximately 40% sulphuric acid can be used. The dilution by the
quantity of wine (here 1.5 ml reagent and 200 .mu.l wine) and other
added reagents must also expediently be taken into
consideration.
[0164] The quantity of sample can also be increased, whereby the
quantities of at least the components 1 and 3 are expediently
increased in the same ratio to the changed sample quantity.
[0165] 2) Determination of the Content of Free SO.sub.2 in
Wine:
Sample volume of wine in the sample container 80, for example
100-300 .mu.l, preferably 150-250 .mu.l
[0166] Component 1: Acid (1-3 ml, preferably 1.25-1.75
ml/sample)
5-20%, preferably 10-15% phosphoric acid with approximately 0.2-5%,
preferably 0.6-0.8% Fe (III) sulphate hydrate
[0167] Higher acid concentrations release too much bound SO.sub.2
and concentrations that are too low yield values that are too low
compared to standard reference methods. The preferred acid
concentration is in the range 5% to 20%. It is also necessary here
to take the dilution by the quantity of wine (here: 1.5 ml reagent
and 200 .mu.l of wine) and possible additional reagents into
consideration. The iron salt is here added only for the reason that
the same line system in the device 100 is used for both variants
(total SO.sub.2 content, content of free SO.sub.2), and thus a
certain corrosion-inhibiting iron content in the device 100 is
assured.
[0168] Component 2: (optional) ammonium sulphate (100-500 mg,
preferably 150-250 mg/sample)
[0169] A salt, which withdraws heat during the dissolution process
can optionally be added, preferably a salt which does not release
any volatile components in combination with acid. Preferred is
ammonium sulphate. If ammonium chloride is used then hydrochloric
acid formed therefrom can be driven out in small quantities by the
carrier gas, and if ammonium nitrate is used then disruptive
nitrogen oxides can be formed.
[0170] Where possible, so much is added that an undissolved residue
remains. This leads to a nearly saturated solution being obtained
with reproducible results. Any errors in the weighing out of
quantities will not play such a large role here. Lower quantities
can naturally also be used, but in this case the weighing-out
should be quantitative.
[0171] The sample (matrix 88 with foreign substance 89) can be
preferably supplied by a metering pipette, for example a
piston-driven pipette. Numerous other variants are, however,
conceivable, such as metering pumps etc. Furthermore, a dilution of
the sample in the system is also conceivable, for instance by
supplying water or dilute acid etc., possibly also in heated form,
possibly also superheated steam as the carrier gas.
[0172] The software used allows detection of possible deviation
from "normal conditions". For example, a deviation of the zero line
is registered, which can mean a contamination of the outside air or
of the system. A carbonate-coated activated charcoal filter can be
used, for example, against contaminated outside air. Purely
mathematically, the basic content of the ambient air can naturally
also be deducted from the measurement result, so that there is
sufficient correction.
[0173] Moreover, the control unit of the device 100 has safety
features, which, for example, bring about disabling of the pump 34
upon incorrect operation or compare the bar code for the reagents
used for conformance with the selected method.
[0174] An error analysis can be carried out for the measurement
curve within certain limits, so that the reliability of the
measurement results is increased. The sensitivity of the sensor 92
can also be checked so that the condition of the sensor 92 is
determined.
[0175] The invention, according to an aspect thereof,
advantageously enables simple handling through pre-dosed components
and a quick analysis through short reaction times. Heating through
the reagent dispenses with the need for expensive components such
as a heating block. The hollow needles of the needle system in the
reagent area have the necessary hardness to enable use in
conjunction with a pierceable septum. Since such systems are
frequently used in other areas, these are available as low cost
materials. A line system of inert materials, such as
[0176] Teflon or other plastics, glass, ceramics and the like is,
however, also conceivable.
* * * * *